UNIT: Oxy-Acetylene; Welding, Brazing, Cutting and Heating

1
UNIT Oxy-Acetylene Welding, Brazing, Cutting
and Heating

• LESSON Oxy-Acetylene Welding (OAW)
• RUNNING A BEAD WITH AND WITHOUT FILLER ROD
• Standard B7.4 Know how to fusion-weld mild
  steel with and without filler rod by using the
  oxy-fuel system

2
The Welding Flame

• A chief advantage of the oxy-acetylene flame is
  its high operating temperatures.
• This oxy-acetylene flame can easily melt all
  common metals.
• The proper mixture of oxygen and acetylene burns
  at 5,589 degrees Fahrenheit, which makes it the
  hottest oxy-fuel gas flame.

3
Types of Flames

• Three types of flames can be produced with the
  oxy-acetylene torch carburizing, neutral, and
  oxidizing.
• The operator must be able to recognize each type
  of flame by its size, shape, and color.
• The operator must also master the adjustment of
  the oxygen and acetylene hand valves on the
  welding torch to produce the desired flame.

4
Carburizing Flame

• Flame contains more acetylene than oxygen.
• This flame is easy to recognize by the outer
  flame, which has a slim bluish taper with an
  orange tip.
• Inside this outer flame is a shorter, blue flame
  called the acetylene feather.
• Flame has a lower temperature than the neutral
  flame.
• Flames are sometimes used for silver brazing,
  braze welding, and soldering.

5
Neutral Flame

• The neutral flame is produced by a proper balance
  of oxygen and acetylene.
• It is approximately 5,589 degrees Fahrenheit and
  is the most widely used of the three types of
  flames.
• As the flame is adjusted from a carburizing flame
  to neutral flame by adding more oxygen, the light
  blue acetylene feather disappears.
• At the same time, the brilliant inner cone
  becomes slightly shorter and more sharply
  defined.

6
Neutral Flame - Cont.

• When a neutral flame is directed upon a steel
  surface, the metal melts slowly.
• The molten metal does not boil and few sparks
  appear.
• The neutral flame protects the molten steel from
  oxidation, and the weld joint is not burned.
• Extremely strong welds are produced from this
  flame.

7
Oxidizing Flame

• Flame contains more oxygen than acetylene.
• Is similar to the shape of the neutral flame,
  however the inner cone of the oxidizing flame is
  more pointed, shorter, and purple.
• The flame can also be distinguished from the
  neutral flame by a loud hissing sound caused by
  the excess rush of oxygen.

8
Oxidizing Flame Cont.

• This flame has very little practical use in
  welding.
• Its temperature may reach 6,300 degrees
  Fahrenheit, but the oxides that form when the
  excess oxygen combines with the molten metal
  cause problems with the weld.
• Such problems include brittleness, weakness, and
  hardening around the weld.

9
Characteristics of the Three Welding Flames
10
Holding the Torch

• A torch may be held in either one of two ways,
  depending on which is the more comfortable for
  you.
• When welding light-gauge metal (under 14 gauge),
  most operators prefer to grasp the handle of the
  torch with the hose over the outside of the
  wrist, in the same manner a pencil ordinarily is
  held.
• In the other grip, the torch is held like a
  hammer, with the fingers lightly curled
  underneath.
• In either case the torch should balance easily in
  the hand to avoid fatigue.

Pencil Grip Method
Hammer Grip Method
11
Pushing a Puddle

• Hold the torch so the flame points in the
  direction you are going to weld and at an angle
  of about 45 degrees with the completed part of
  the weld.
• If you are right handed, start the weld at the
  right edge of the metal and bring the inner cone
  of the neutral flame to within 1/8 of the
  surface of the plate.
• The left-handed person reverses this direction.
• Hold the torch still until a pool of molten metal
  forms.
• Then move (push) the puddle across the plate.

12
Pushing a Puddle Cont.

• As the puddle travels forward, rotate the torch
  to form a series of overlapping ovals or circles
  (forming a bead)
• Do not move the torch ahead of the puddle, but
  slowly work forward, giving the heat a chance to
  melt the metal.
• If the flame is moved forward too rapidly, the
  heat fails to penetrate far enough and the metal
  does not melt properly.
• If the torch is kept in one spot too long, the
  flame will burn a hole through the metal.

13
Laying a bead with filler rod

• On some types of joints (outside corner welds) it
  is possible to weld the two pieces of metal
  without adding metal from a filler rod.
• The use of a filler rod requires coordination of
  the two hands.
• One hand must manipulate the torch to carry a
  puddle across the plate, while the other hand
  must add the correct amount of filler rod.
• In most instances the use of a filler rod is
  advisable because it builds up the weld, thereby
  adding strength to the joint.
• The strength of a weld depends largely on the
  skill with which the rod is blended, or
  interfused, with the edges of the base metal.

14
Selecting the filler rod

• Filler rods come in a variety of sizes ranging
  from 1/16 to 3/8 in diameter.
• The size of rod to use will depend largely upon
  the thickness of the metal being welded.
• The general rule is to use a rod with a diameter
  equal to the thickness of the base metal.
• In other words, if a 1/16 metal is being welded,
  a 1/16 diameter rod should be used.

15
Laying a bead with filler rod Cont.

• The torch is held at an angle of approximately 45
  degrees to the base metal, hold the rod at
  approximately the same angle as the torch but
  slant it away from the torch.
• Move the torch tip over the starting edge and
  rotate the flame near the metal in a circular or
  semicircular motion until the base metal melts
  into a small puddle.
• Once a small pool of the base metal is
  established, dip the tip of the rod in the molten
  pool.
• ALWAYS DIP THE ROD IN THE CENTER OF THE MOLTEN
  POOL.

16
Laying a bead with filler rod Cont.

• The molten puddle will melt the rod and add to
  the puddle, as the rod melts in the pool, advance
  the torch forward.
• Concentrate the flame on the base metal and not
  on the rod.
• Do not hold the rod above the pool. If you do
  this the molten metal will fall through the air
  to the puddle.
• When this happens it combines with the oxygen in
  the air and part of it burns up, causing a weak,
  porous weld.

17
Common Difficulties with Laying a Bead with
Filler Rod .

• The beginner often experiences difficulty in
  holding the welding rod steady which can cause
  the rod to stick to the base metal
• Instead of inserting the rod in the middle of the
  puddle where the heat is sufficient to melt it
  readily, a beginner generally inserts the rod
  near the edge of the pool where the temperature
  is lower. The heat at the edge is not enough to
  melt the rod and the rod will likely stick to the
  base metal.
• If the rod sticks to the base metal, do not try
  to jerk it loose.
• Simply place the flame directly over the tip of
  the rod and the rod will be freed immediately.

18
Laying a bead with filler rod Cont.

• The circular or semicircular motion should be
  advanced approximately 1/16 per motion until the
  end of the joint is reached.
• Since the angle of the tip flame is preheating
  the metals ahead of the weld, the last ½ of weld
  is critical.
• Slightly raise the welding tip and increase the
  addition of filler rod to insure a full smooth
  weld.

19
Bead with filler rod

• Bead with Filler Rod
• Push a Puddle (No filler rod)